Non-intrusive modem performance analysis

ABSTRACT

A method of analyzing the performance of a modem connection. The method includes connecting a line interface to a communication link carrying signals of a modem connection, between a pair of end modems, collecting signals passing on the communication link, between the end modems, through the line interface, determining quality or transmission characteristics regarding the modem connection, responsive to signals collected through the line interface, and displaying information on the determined characteristics.

FIELD OF THE INVENTION

The present invention relates to communication systems and in particularto modem communication systems.

BACKGROUND OF THE INVENTION

Digital networks are used to transfer computer data and other signalsbetween computers and other end apparatus. In connecting home users todigital networks, analog lines are commonly used. In transmitting dataover analog lines, modems on opposite sides of the analog lines modulatethe transmitted signals on one side and demodulate the transmittedsignals on the other side.

In order to allow the end modems to communicate, protocols define theprecise signals to be transmitted by the modems. These protocolsinclude, among others, voice band modem (VBM) protocols which use thefrequency band allocated to voice signals and DSL protocols (e.g., ADSL)which use-much larger portions of the frequency band of the analog line.

Some of the defined protocols are very complex, so as to achieve maximalutilization of the available bandwidth. Due to the complexity of themodem protocols, there are cases in which different vendors implementthe protocols differently, leading in some cases to problems incommunications.

Modem emulators are sometimes used to test the operation of modems. Amodem emulator is connected on an opposite side of a communication lineto which the tested modem is connected, transmits testing signal to thetested modem and provides a report on the operation of the tested modem.Another existing tool for testing modems is a pair of scope modems whichare connected in the middle of a tested analog line connecting oppositeend modems. Each modem in the pair of scope modems connects to adifferent one of the opposite end modems, forming a double connection.The pair of scope modems mirror data between the connections and providethe transferred data to an upper layer for analysis.

For security reasons it may be desired to listen to communication linesof suspected individuals. When the communication lines carry modemsignals, the signals are generally demodulated in order to determinetheir content. The demodulation is a relatively hard task, especially ifthe demodulation is performed by a passive unit, which cannot requestretransmissions and cannot adjust the transmission levels according tothe noise level in the vicinity of the eavesdropping apparatus.Therefore, when possible, eavesdropping is performed on signals whichare not modulated (e.g., already demodulated). Most VBM connections areestablished with an Internet Service provider (ISP) and eavesdroppingcan be performed by the ISP. Modem connections, however, can beestablished between two private modems. In such connections, it is notalways known, for a monitored modem, where the other end modem is and itis not always possible to access that modem.

The signals of ADSL connections, on the other hand, are alwaysdemodulated by a modem at a local line-card of a telephone servicecompany, and when necessary can be monitored at the line-card.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates to aperformance analyzer for modem connections, optionally full-duplex modemconnections, which analyzes the operation of a modem connection betweena pair of modems. The performance analyzer does not replace the modemsof the connection, but rather listens to the communications on the modemconnection. In some embodiments of the invention, the modem performanceanalyzer passively listens to the signals transmitted between a pair ofmodems without sending acknowledgment signals or any other modemtangible signals to either of the modems. Optionally, the performanceanalyzer may inject noise on the communication line of the connection,at specific times, in order to cause a retrain of the connection. Theperformance of a retrain may aid in better understanding the signalspassing on the connection and/or in identifying connection parameters.

The performance analyzer optionally provides information on at least oneparameter of the physical operation of the connection, such as the powerspectrum density (PSD), discrete multi-tone (DMT) mapping, noiseparameters of the line and line quality. Alternatively or additionally,the performance analyzer provides information on non-data signalspassing on the connection, such as negotiation signal content, and/orsignaling signals passing in parallel to the data transferred on theline, for example AOC (ADSL overhead control) signals, embeddedoperating channel (EOC) signals and/or indicator bits (IB).

In some embodiments of the invention, the performance analyzer providesinformation on the modem connection in different physical operationlayers and shows cross-references between the different physical layers.Optionally, the performance analyzer provides information on possibleconnections between data retransmissions or connection retrains andnoise effects or other modem acts which caused the retransmissions orretrains.

An aspect of some embodiments of the invention relates to third-partyapparatus adapted to force a retrain on an XDSL connection of a twistedpair line, without obstructing telephone service on the twisted pairline. Optionally, the apparatus does not participate in the xDSLconnection. In some embodiments of the invention, the apparatuscomprises a performance analyzer and/or an eavesdropper which passivelylistens to the XDSL connection. Forcing a retrain is optionally used todetermine parameters of the XDSL connection, required for properinterpretation of the signals passing on the connection.

An aspect of some embodiments of the invention relates to an ADSLeavesdropping system which passively listens to signals passing on theconnection.

There is therefore provided in accordance with an exemplary embodimentof the invention, a method of analyzing the performance of a modemconnection, comprising connecting a line interface to a communicationlink carrying signals of a modem connection, between a pair of endmodems, collecting signals passing on the communication link, betweenthe end modems, through the line interface, determining quality ortransmission characteristics regarding the modem connection, responsiveto signals collected through the line interface, and displayinginformation on the determined characteristics.

Optionally, the modem connection comprises a full-duplex modemconnection. Optionally, the modem connection comprises an ADSL modemconnection. Optionally, connecting the line interface to thecommunication line comprises connecting at a point at least two timescloser to one of the modems than the other modem. Optionally, connectingthe line interface to the communication line comprises connecting at apoint at most two times closer to one of the modems than to the othermodem. Optionally, collecting signals passing on the communication linkcomprises collecting without sending to either of the modemsacknowledgment signals or any other modem tangible signals. Optionally,displaying information on the determined characteristics comprisesdisplaying the contents of one or more modem negotiation signals.

Optionally, displaying information on the determined characteristicscomprises providing information on noise levels on the connection.Optionally, providing information on noise levels on the connectioncomprises suggesting possible sources of the noise. Optionally,displaying information on the determined characteristics comprisesproviding information on effects in upper physical layers caused by thenoise levels on the connection.

Optionally, displaying information on the determined characteristicscomprises providing information on the symbol mapping used by theconnection. Optionally, displaying information on the determinedcharacteristics comprises displaying information on signaling signalstransmitted in parallel to data transmission; Optionally, the methodincludes performing signal tests on test signals transmitted on theconnection and comparing the results of the tests to negotiation signalsreporting test results from one of the modems. Optionally, the methodincludes injecting by the performance analyzer noise which forces aretrain of the modem connection.

Optionally, injecting the noise comprises injecting noise in a mannerwhich does not substantially interfere with a different connectionpassing on the communication link. Optionally, injecting the noisecomprises connecting a low impedance circuit, for at least some of thefrequency bands carrying signals, to the communication link Optionally,the modem connection comprises a DSL connection. Optionally, theinjected noise does not interfere with voice frequency bands of thecommunication link. Optionally, the modem connection comprises a voiceband modem connection. Optionally, the method includes identifyingchanges in the operation of the modem connection and providing suggestedcauses of the changes.

Optionally, identifying changes comprises identifying a retrain and/or abit swap. Optionally, providing suggested causes of the changescomprises identifying, for at least one change, a noise that caused thechange. Optionally, the method includes identifying data retransmissionsand providing suggested causes of the data retransmissions. Optionally,displaying information on the determined characteristics comprisesdisplaying a raw bit content of signals transmitted on the modemconnection. Optionally, displaying information on the determinedcharacteristics comprises providing a warning on a possible tapping ofthe communication link. Optionally, the method includes extracting thedata transmitted on the modem connection.

There is further provided in accordance with an exemplary embodiment ofthe invention, a modem connection performance analyzer, comprising aline interface adapted to collect signals of a modem connection passingon a communication link, between two end modems connected to the link, aprocessor adapted to determine one or more quality or transmissioncharacteristics regarding the modem connection, responsive to thecollected signals, and a human interface adapted to provide informationon the determined characteristics. Optionally, the performance analyzerincludes a low impedance shorting circuit adapted to short at least someof the frequencies of the communication link, responsive to a commandfrom the processor.

There is further provided in accordance with an exemplary embodiment ofthe invention, a method of monitoring an xDSL modem connection,comprising connecting a line interface to a communication link carryingsignals of an XDSL modem connection, between a pair of end modemsseparate from the line interface, collecting signals passing between theend modems on the communication link, through the line interface, andproviding information on the modem connection, responsive to thecollected signals.

Optionally, providing information on the modem connection comprisesproviding information on the operation of the connection and/orproviding data passing on the connection.

There is further provided in accordance with an exemplary embodiment ofthe invention, a method of forcing a retrain on a modem connection,comprising determining at least one first frequency band to bedisrupted, and connecting to a communication line carrying the modemconnection, between two end modems, a circuit which disruptstransmission of signals on the at least one first frequency band.Optionally, determining the at least one first frequency band to bedisrupted comprises determining a frequency band including a pilot tonefrequency band of the modem connection. Optionally, the circuit disruptsthe first frequency band substantially without interfering with signalsof a second frequency band. Optionally, the second frequency bandcomprises a frequency band of voice signals. Optionally, connecting thedisruption circuit comprises connecting a circuit which shorts the atleast one first frequency band without shorting the second frequencyband. Optionally, connecting the disruption circuit comprises connectinga circuit which injects noise at the at least one first frequency band.

BRIEF DESCRIPTION OF FIGURES

Particular non-limiting embodiments of the invention will be describedwith reference to the following description of embodiments inconjunction with the figures. Identical structures, elements or partswhich appear in more than one figure are preferably labeled with a sameor similar number in all the figures in which they appear, in which:

FIG. 1 is a schematic illustration of a performance analyzer connectedto an ADSL connection, in accordance with an exemplary embodiment of theinvention;

FIG. 2 is a schematic block diagram of a performance analyzer, inaccordance with an exemplary embodiment of the invention;

FIG. 3 is a schematic block diagram illustrating the operation of achannel analyzer, in accordance with an exemplary embodiment of theinvention;

FIGS. 4A-4D are schematic screen views provided by a graphic userinterface, in accordance with an exemplary embodiment of the invention;and

FIGS. 5A and 5B are schematic block diagrams of channel separators, inaccordance with exemplary embodiments of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a schematic illustration of a performance analyzer 102connected to an ADSL connection 100, in accordance with an exemplaryembodiment of the invention. ADSL connection 100 is typicallyestablished over a twin pair line 104, which generally connects a clientlocation 120 to a line-card 122 of a public telephone network. A clientmodem 110 connects to twin pair line 104 at a first end, in clientlocation 120, and a server modem 112 (referred to also as a DSLAM),connects to twin pair line 104 at a second end, in the location ofline-card 122. In some embodiments of the invention, ADSL connection 100operates according to a protocol which uses different frequency bandsfor upstream and downstream transmission. Alternatively, as describedbelow with reference to FIG. 5B, ADSL connection 100 may operateaccording to a protocol including overlapping frequency bands, and timeseparation, for upstream and downstream signals.

FIG. 2 is a schematic block diagram of performance analyzer 102, inaccordance with an exemplary embodiment of the invention. Performanceanalyzer 102 optionally includes a line interface 202 which connects totwin pair line 104 and senses the signals thereon. Line interface 202optionally includes a high-impedance low-noise interface suitable forsensing signals from line 104 without interfering with the signalstransmitted on the line. The sensed signals from line interface 202 areoptionally provided to an A/D converter and channel separation unit 204,which separates the sensed signals into upstream and downstream signalsand converts the sensed analog signals into digital samples. Theupstream and downstream digital samples are provided, respectively, toan upstream analyzer 206 and a downstream analyzer 210, which analyzethe data of their respective channel, as described in detail below. Acontroller 220 optionally receives information from both upstreamanalyzer 206 and downstream analyzer 210 and generates combined analyzeddata. Examples of the combined analyzed data are described below. Insome embodiments of the invention, controller 220 additionally controlsthe operation of upstream analyzer 206, downstream analyzer 210 and/orA/D converter and channel separation unit 204.

Optionally, the samples and/or analysis results are stored on a storagemedia 208, for further reference and/or for comparison to later receivedsignals. A graphic user interface (GUI) 212 optionally displays the rawdigital samples and/or the analyzed data. Optionally, a user may selectwhich data is to be stored and/or displayed. Alternatively oradditionally, the user may control other functions of performanceanalyzer 102, such as when alerts are provided and/or when retrains areto be initiated. Optionally, performance analyzer 102 may be configuredto monitor only some of the signals passing on the connection. In anexemplary embodiment of the invention, performance analyzer 102 may beconfigured only to monitor retrains, only to monitor show-timetransmission, or to perform continuous monitoring. In some embodimentsof the invention, the raw signals and/or analyzed data are transmittedto a remote unit for further analysis and/or for display.

In some embodiments of the invention, an interruption generator 214 isadapted to provide a noise signal on line 104, so as to induce a retrainof the modem connection. Optionally, interruption generator 214 providesa noise which does not affect low frequencies of the channel, which arededicated for carrying regular telephone connections. Optionally,interruption generator 214 provides a noise on one or more specificfrequencies, which noise disrupts the entire ADSL connection. In someembodiments of the invention, interruption generator 214 provides anoise-on the pilot tone frequency of DSL connections, e.g., 276 kHz.

Alternatively or additionally, noise is provided in a plurality offrequencies so that a retrain is forced regardless of the type of DSLconnection used and/or the exact frequencies currently used for datatransmission. For example, the provided noise may include a wide bandnoise with a relatively high amplitude.

Alternatively or additionally, interruption generator 214 shorts line104 for high frequencies, by connecting a low impedance connection forhigh frequencies, to line 104. The use of a low impedance short in orderto initiate a retrain makes it harder to identify the source of theretrain. In addition, the short does not include actively generatednoise which may interfere with neighboring lines to which the short isnot directly connected.

FIG. 3 is a schematic block diagram illustrating the operation of ananalyzer 300, which may be used in implementing upstream analyzer 206and/or downstream analyzer 210, in accordance with an exemplaryembodiment of the invention. A state machine 302 optionally keeps trackof the state of the modem connection, for example whether the connectionis carrying data or initialization and activation signals. State machine302 optionally further keeps track of the frequency bands used fortransferring data, the bit rates used in each frequency band and/or thesignal mappings used State machine 302 optionally receives data fromother units of analyzer 300 (for simplicity connections are not shown)and accordingly keeps track of the state of the connection. Ademodulator 304 optionally receives the signals of the connection fromchannel separation unit 204 and converts them into bits, according tothe current state of the modem connection as tracked by state machine302. In some embodiments of the invention, - a noise determination unit306 determines the noise spectrum on the connection, based on acomparison of a theoretical re-modulation of the converted bits to theactually received signals. Optionally, a noise characterizer 308attempts to determine the type of the noise according to the noisespectrum, for example by comparing the determined noise spectrum topredetermined known spectrums.

During initialization and activation, an initialization analyzer 310optionally receives the demodulated bits and forms therefrom a map ofthe initialization process. Accordingly, state machine 302 is optionallyupdated.

In some embodiments of the invention, when known training signals aretransmitted from one of the modems, to allow the other modem to evaluatethe line, a channel testing unit 320 analyzes the training signals todetermine the channel quality, in a manner similar to that performed bythe end modems of the connection. The results of the channel testing areoptionally compared to the results transmitted by the end modem (110 or112 in FIG. 1) receiving the testing signals. According to thecomparison, testing-signal analyzer 310 optionally determines therelative positioning of performance analyzer 102 on twin pair line 104,and/or evaluates the operation of the end modem.

During data transfer (also referred to as show time), a signalinganalyzer 312 optionally receives the demodulated bits and extracts fromthem signaling bits which are transmitted along with the data. Signalinganalyzer 312 optionally generates a map of the signaling signals andaccordingly updates state machine 302, when appropriate. Alternativelyor additionally, signaling analyzer 312 directly updates demodulator 304on changes which relate to the demodulation, when necessary. In thisalternative, state machine 302 may be omitted from analyzer 300 or maybe included in demodulator 304 or controller 330. For example, thesignaling bits may indicate a change in the utilization of the channelfrequencies, and this data is required for the demodulation.

The signaling bits transferred during the show time stage (e.g., AOC,EOC and/or indicator bits) from analyzer 312 are optionally provided tocontroller 220 for display to the user and/or for verifying correctperformance of the end modems. In some embodiments of the invention,when the signaling bits indicate a change in the transmission, such as abit swap, controller 220 suggests possible causes of the change.

In some embodiments of the invention, a data analyzer 314 determines thedata content of the received data bits, performing one or more higherlayer tasks. Alternatively, the data content is not determined, so thatperformance analyzer 102 can be used without affecting the privacy ofthe users of the modem.

A controller 330 optionally controls the transfer of signals fromdemodulator 304 to the other elements of analyzer 300, for exampleaccording to the state of state machine 302.

Referring in more detail to demodulator 304, in some embodiments of theinvention, the demodulation includes a trellis operation, during datatransfer. Optionally, demodulator 304 keeps track of the operation ofthe trellis decoding and provides indications on the trellis decoding tocontroller 220 for display to the user. For example, in some cases wheniterative decoding is used, demodulator 304 may track the number oftrellis rounds required for correct demodulation and/or the number ofsamples having values corrected during traversing the trellis. In someembodiments of the invention, demodulator 304 performs trellis decodingusing different methods and reports which decoding methods weresufficient to demodulate the signals correctly and which methods werenot able to achieve a correct result. In other embodiments of theinvention, no information is provided to the user from the trellisdecoding. Optionally, when the protocol requires a trellis decoding orallows a trellis decoding, performance analyzer 102 includes a processorsuitable for performing the trellis decoding efficiently and quickly.

Alternatively or additionally, demodulator 304 keeps track of otherdemodulation parameters, such as filter coefficients, mapper pointsand/or Reed Solomon performance. In some embodiments of the invention,demodulator 304 is adapted to identify retrain signals and accordinglyto update state machine 302. In some embodiments of the invention,demodulator 304 also provides data on the power spectrum density of thesignals.

Referring in more detail to noise determination unit 306, in someembodiments of the invention, noise determination unit 306 accumulatesnoise values for data blocks of a predetermined size and for each datablock determines noise statistics, for example noise levels for eachfrequency band. Optionally, noise determination unit 306 is adapted toidentify unusual noise levels and/or events and characterize the noises,for example as impulse noises, cross-talk noises or attenuations. Noisecharacterizer 308 optionally compares the determined noise statistics topredetermined noise spectrums of known events. In an exemplaryembodiment of the invention, noise characterizer 308 stores noisespectrums of interference events, such as from wireless sources,adjacent wire communication lines, radio sets and electric appliances.Alternatively or additionally, noise characterizer 308 is pre-configuredwith expected affects of temperature changes on the noise level and/orattenuation causes. In some embodiments of the invention, noisecharacterizer 308 is configured with expected spectrums of purposelyadded noise, for example noise added by a line tapping unit. Optionally,controller 220 provides a warning on possible tapping units on line 104.

In some embodiments of the invention, when a possible tapping isidentified, performance analyzer 102 provides indications on theprobable location of the tapping unit, for example based on the timingand/or amplitude of the tapping noise. Alternatively or additionally,when performance analyzer 102 identifies a first sign of a possibletapping unit, the performance analyzer keeps track of additional signsin the received signals which indicate presence of the tapping unit.

In some embodiments of the invention, performance analyzer 102 activelytransmits test signals on the line to identify whether a tapping unit isconnected to line 104. Alternatively or additionally, performanceanalyzer 102 may be configured to prevent any transmissions on lines 104when a tapping is identified, in order to prevent leakage of secretinformation.

Optionally, for each block having an irregular noise pattern, noisecharacterizer 308 provides controller 220 with one or more possiblereasons for the irregularity in the noise.

Noise determination unit 306 is optionally adapted to determine theattenuation level caused by lines 104, for example by comparing thelevel of the received signals to the known transmitted level.Alternatively or additionally, noise determination unit 306 determinesthe signal to noise ratio of the signals.

In some embodiments of the invention, controller 220 provides warningson incorrect behavior of the end modems. Optionally, controller 220follows transmission threads of the modems and provides a warning whenone of the modems performs differently than required by the governingprotocol. For example, when a modem is requested to change the frequencybands it uses for data transmission, controller 220 verifies that themodem moved at the correct time to the new band division. In anotherexample, controller 220 follows the negotiation signals transmittedbetween the modems and provides a warning when the signals are differentthan prescribed by the governing protocol.

Optionally, controller 220 also searches for lower layer causes ofproblematic higher layer effects. For example, when a retransmission ofdata is requested, controller 220 optionally searches to see if, at thetime the original data was transmitted, there was an interference dn theline, such as an unusual noise level, a low signal to noise ratio (SNR),a high attenuation level and/or if the modem suffered from skew or otherproblematic effects in some embodiments of the invention, suggestedcauses are provided for other identified higher layer problems, such asCRC errors, corrupted bits, and/or low performance of Reed Solomondecoding. In some embodiments of the invention, when one of the modemsrequests a change in the bit allocation of the frequency band,controller 220 determines the cause of the request and whether therequest was necessary.

Alternatively or additionally, controller 220 indicates higher layereffects caused by lower layer problems, such as impulse noises and/orcross-talk noises (e.g., from other ADSL lines, from wirelesstransmissions and/or from regular telephone use). In some embodiments ofthe invention, controller 220 provides statistics on the stability ofthe connection. For example, controller 220 may provide indication ofthe percentage of cases in which an impulse noise causes higher layertrouble and/or the average rate at which higher layer problematic eventsoccur.

In some embodiments of the invention, controller 220 is adapted tocompare signal exchanges of one connection with signal exchanges ofprevious connections. For example, a test session may include connectinga plurality of different modems to a tested modem and comparing thetraining sessions of the different connections.

Optionally, a user may request controller 220 to display data fromprevious connections, optionally showing an entire connection.

FIGS. 4A-4D are schematic screen views provided by GUI 212, inaccordance with an exemplary embodiment of the invention. In FIG. 4A, ascreen 520 shows a general high level overview of a monitoredconnection. Screen 520 lists the stages (phases) of the connection andoptionally the protocols governing each of the stages. For eachoperation stage (phase) of the connection, a user may optionally requestadditional details. For example, responsive to a request for additionaldetails about a negotiation phase, a screen 500 (FIG. 4B) which shows aportion of an ADSL initialization stage, is optionally shown. Screen 500optionally includes a downstream portion 502 and an upstream portion504. The name 506 of each signal transmitted on the connection isoptionally displayed with its beginning 508 and ending 510 transmissiontimes and/or the number 512 of samples it includes. Optionally, thesignals of the upstream and downstream are displayed with timecorrelation, such that a viewer can easily determine the signal timeline of the connection. In some embodiments of the invention, a user mayclick on any of the signal names to view more details about the signal.

A screen 540 (FIG. 4C) optionally displays the spectrum, magnitude 544and phase 546 of the transmitted signals. Optionally, a user may selectwhether to view upstream and/or downstream signals 548, the type of view(e.g., spectrum) 541 and/or the processing stage 549 at which thespectrum signals are viewed. In some embodiments of the invention, theuser may select whether to view the spectrum before they undergo timedomain equalization (TEQ), fast Fourier transformation (FFT), frequencydomain equalization (FEQ) or after the FEQ. Optionally, the user mayselect the time duration for which the spectrum may be viewed. The usermay select one or more signals for which the spectrum is to be displayedfrom bar 543 and/or may select one or more time blocks from bar 542.

In some embodiments of the invention, a screen 560 (FIG. 4D) lists thefields of each signal and the bit content of each field with anexplanation of the value of each field. Optionally, a screen 570 showsthe properties of line 104. Optionally, an upstream graph 571 and adownstream graph 507 (shown only partially) show the transfer function572 and the noise form 574 of the communication line. Graphs 575 and 577optionally show the respective phases.

In some embodiments of the invention, a screen 580 shows the position ofperformance analyzer 102 along line 104. The position is optionallyestimated based on the signals received by performance analyzer 102.

FIG. 5A is a schematic block diagram of A/D converter and channelseparation unit 204, in accordance with an exemplary embodiment of theinvention. Unit 204 optionally includes an upstream processing path 404and a down stream processing path 406. At the entrance to upstream path404, an up stream filter 410 filters the sensed signals allowing onlysignals belonging to the upstream band to pass (in exemplary protocolsknown in the art, signals. between 27-138 kHz). Optionally, upstreamfilter 410 allows additional signals at marginal frequencies to passthrough the filter so as not to loose any data. The upstream signals arepassed through an automatic gain controller (AGC) 414 and an analog todigital converter (A/D) 416, which converts the signals into digitalsamples. The digital samples are optionally passed to an estimator 418which removes affects of the downstream on the upstream signals, usingmethods known in the art.

In parallel, the sensed signals are optionally passed to a downstreamfilter 412 which passes only signals that belong to the downstreamchannel, optionally with additional margins. The downstream signals aretransferred through an AGC 424 and an A/D 426, which converts thedownstream signals into digital samples. The digital samples of thedownstream are passed to an estimator 428 which removes affects of theupstream on the downstream signals, using methods known in the art.

In some embodiments of the invention, if necessary according to theprotocol governing the transmission of signals on lines 104, the bandsof filters 410 and 412 are adjustable according to the currenttransmission conditions on the lines.

Optionally, for additional accuracy, estimators 430 are also included inunit 204 to remove residue cross-talk between the upstream anddownstream channels, as is known in the art. The cleaned upstream anddownstream signals are optionally passed to their respective signalanalysis units 206 and 210 (FIG. 2).

FIG. 5B is a schematic block diagram of an overlap cancellation unit 450to be used instead of AID converter and channel separation unit 204, inaccordance with an exemplary embodiment of the invention. Overlapcancellation unit 450 is optionally used when ADSL connection 100carries signals according to a protocol including overlapping frequencybands for upstream and downstream signals. Overlap cancellation unit 450optionally includes an analog circuit 452, which converts the signalsfrom line interface 202 into digital samples. The digital samples areoptionally provided to separate upstream and downstream processors 454and 456 which estimate the signals of their respective channel, forexample according to the different amplitudes of the channels. Theestimations from the processors 454 and 456 and optionally provided tocross-talk cancellers 458 which reduce the estimations of the oppositechannel from the signals provided to the processors.

In some embodiments of the invention, the estimation performed byprocessors 454 and 456 are repeated several times, to achieve a goodchannel separation. Optionally, the estimation is repeated until anerror rate below a predetermined value is achieved and/or until anachieved correction between two consecutive iterations is smaller than apredetermined level. Alternatively or additionally, a predeterminednumber of iterations is performed.

Alternatively or additionally, to differentiating between the signals inthe upstream and downstream according to their amplitude, the signalsare separated according to the timings of the signals. Optionally,overlap cancellation unit 450 keeps track of and/or receives data fromother units of performance analyzer 102 and accordingly the upstream anddownstream signals are separated. For example, when some of thefrequency bands do not overlap, the signals in overlapping frequenciesare separated according to which of the upstream or downstream bandshave signals at the same time. Alternatively or additionally, thesignals are separated according to the stream to which the signalsimmediately preceding or following in time, belong.

In some embodiments of the invention, controller 220 operatesindependently from unit 204 or 450. Alternatively, one or moreparameters determined by unit 204 or 450, such as the AGC gain level isprovided to controller 220 and is used in evaluating the connectionand/or is displayed by GUI 212.

Performance analyzer 102 is optionally positioned close to client modem110 or close to server modem 112. Positioning performance analyzer 102close to one of the modems may allow simpler separation of the upstreamand downstream signals. Alternatively, performance analyzer 102 ispositioned at a middle point between the modems so that neither of theupstream and downstream signals in maximally attenuated. It is notedthat since, in some embodiments of the invention, performance analyzer102 is passive and, for example, does not request retransmissions,avoidance of high attenuation is required to a greater extent than forthe end modems.

Although the above description relates to an ADSL connection, theinvention is not limited to any specific modem connection, and may beused with other DSL connections as well as other modem connections, suchas VBM connections.

In some embodiments of the invention, performance analyzer 102 is usedin testing modems for standard compliance and/or in testing a pair ofmodems for interoperability assurance. Alternatively or additionally,performance analyzer 102 is used in modem testing and/or debugging.Further alternatively or additionally, performance analyzer 102 is usedin troubleshooting, quality of service (QoS) monitoring, modemqualification and/or rating, communication system maintenance and/or forgeneral performance analysis.

The elements of performance analyzer may be implemented using dedicatedhardware or may be implemented by a combination of software andhardware. For example, analyzer 300 may be implemented in software on asingle general purpose computer or on a plurality of dedicated orgeneral purpose processors. Each element of analyzer 300 maybeimplemented by a separate software module or some or all of the elementsof analyzer 300 maybe implemented by a single software module.Alternatively or additionally, different task divisions than thosedescribed above may be used.

It will be appreciated that the above described methods may be varied inmany ways, including, changing the order of steps, and/or performing aplurality of steps concurrently. It should also be appreciated that theabove described description of methods and apparatus are to beinterpreted as including apparatus for carrying out the methods, andmethods of using the apparatus. The screen shots shown in FIGS. 4A-4Dwere presented by way of example and many other views may be used inaccordance with the present invention. The present invention has beendescribed using non-limiting detailed descriptions of embodimentsthereof that are provided by way of example and are not intended tolimit the scope of the invention. It should be understood that featuresand/or steps described with respect to one embodiment may be used withother embodiments and that not all embodiments of the invention have allof the features and/or steps shown in a particular figure or describedwith respect to one of the embodiments. Variations of embodimentsdescribed will occur to persons of the art. Furthermore, the terms“comprise,” “include,” “have” and their conjugates, shall mean, whenused in the claims, “including but not necessarily limited to.”

It is noted that some of the above described embodiments may describethe best mode contemplated by the inventors and therefore may includestructure, acts or details of structures and acts that may not beessential to the invention and which are described as examples.Structure and acts described herein are replaceable by equivalents whichperform the same function, even if the structure or acts are different,as known in the art. Therefore, the scope of the invention is limitedonly by the elements and limitations as used in the claims.

1. A method of analyzing the performance of a modem connection,comprising: connecting a line interface to a communication link carryingsignals of a modem connection, between a pair of end modems; collectingsignals passing on the communication link, between the end modems,through the line interface; determining quality or transmissioncharacteristics regarding the modem connection, responsive to signalscollected through the line interface; and displaying information on thedetermined characteristics.
 2. A method according to claim 1, whereinthe modem connection comprises a full-duplex modem connection.
 3. Amethod according to claim 1, wherein the modem connection comprises anADSL modem connection.
 4. A method according to claim 1, whereinconnecting the line interface to the communication line comprisesconnecting at a point at least two times closer to one of the modemsthan the other modem.
 5. A method according to claim 1, whereinconnecting the line interface to the communication line comprisesconnecting at a point at most two times closer to one of the modems thanto the other modem.
 6. A method according to claim, wherein collectingsignals passing on the communication link comprises collecting withoutsending to either of the modems acknowledgment signals or any othermodem tangible signals.
 7. A method according to claim 1, whereindisplaying information on the determined characteristics comprisesdisplaying the contents of one or more modem negotiation signals.
 8. Amethod according to claim 1, wherein displaying information on thedetermined characteristics comprises providing information on noiselevels on the connection.
 9. A method according to claim 8, whereinproviding information on noise levels on the connection comprisessuggesting possible sources of the noise.
 10. A method according toclaim 8, wherein displaying information on the determinedcharacteristics comprises providing information on effects in upperphysical layers caused by the noise levels on the connection.
 11. Amethod according to claim 1, wherein displaying information on thedetermined characteristics comprises providing information on the symbolmapping used by the connection.
 12. A method according to claim 1,wherein displaying information on the determined characteristicscomprises displaying information on signaling signals transmitted inparallel to data transmission.
 13. A method according to claim 1,comprising performing signal tests on test signals transmitted on theconnection and comparing the results of the tests to negotiation signalsreporting test results from one of the modems.
 14. A method according toclaim 1, comprising injecting by the performance analyzer noise whichforces a retrain of the modem connection.
 15. A method according toclaim 14, wherein injecting the noise comprises injecting noise in amanner which does not substantially interfere with a differentconnection passing on the communication link.
 16. A method according toclaim 14, wherein injecting the noise comprises connecting a lowimpedance circuit, for at least some of the frequency bands carryingsignals, to the communication link.
 17. A method according to claim 14,wherein the modem connection comprises a DSL connection.
 18. A methodaccording to claim 17, wherein the injected noise does not interferewith voice frequency bands of the communication link.
 19. A methodaccording to claim 1, the modem connection comprises a voice band modemconnection.
 20. A method according to claim 1, comprising identifyingchanges in the operation of the modem connection and providing suggestedcauses of the changes.
 21. A method according to claim 20, whereinidentifying changes comprises identifying a retrain.
 22. A methodaccording to claim 20, wherein identifying changes comprises identifyinga bit swap.
 23. A method according to claim 20, wherein providingsuggested causes of the changes comprises identifying, for at least onechange, a noise that caused the change.
 24. A method according to claim1, comprising identifying data retransmissions and providing suggestedcauses of the data retransmissions.
 25. A method according to claim 1,wherein displaying information on the determined characteristicscomprises displaying a raw bit content of signals transmitted on themodem connection.
 26. A method according to claim 1, wherein displayinginformation on the determined characteristics comprises providing awarning on a possible tapping of the communication link.
 27. A methodaccording to claim 1, comprising extracting the data transmitted on themodem connection.
 28. A modem connection performance analyzer,comprising: a line interface adapted to collect signals of a modemconnection passing on a communication link, between two end modemsconnected to the link; a processor adapted to determine one or morequality or transmission characteristics regarding the modem connection,responsive to the collected signals; and a human interface adapted toprovide information on the determined characteristics.
 29. A performanceanalyzer according to claim 28, comprising a low impedance shortingcircuit adapted to short at least some of the frequencies of thecommunication link, responsive to a command from the processor.
 30. Amethod of monitoring an xDSL modem connection, comprising: connecting aline interface to a communication link carrying signals of an xDSL modemconnection, between a pair of end modems separate from the lineinterface; collecting signals passing between the end modems on thecommunication link, through the line interface; and providinginformation on the modem connection, responsive to the collectedsignals.
 31. A method according to claim 30, wherein providinginformation on the modem connection comprises providing information onthe operation of the connection.
 32. A method according to claim 30,wherein providing information on the operation of the modem connectioncomprises providing data passing on the connection.
 33. A method offorcing a retrain on a modem connection, comprising: determining atleast one first frequency band to be disrupted; and connecting to acommunication line carrying the modem connection, between two endmodems, a circuit which disrupts transmission of signals on the at leastone first frequency band.
 34. A method according to claim 33, whereindetermining the at least one first frequency band to be disruptedcomprises determining a frequency band including a pilot tone frequencyband of the modem connection.
 35. A method according to claim 33,wherein the circuit disrupts the first frequency band substantiallywithout interfering with signals of a second frequency band.
 36. Amethod according to claim 35, wherein the second frequency bandcomprises a frequency band of voice signals.
 37. A method according toclaim 35, wherein connecting the disruption circuit comprises connectinga circuit which shorts the at least one first frequency band withoutshorting the second frequency band.
 38. A method according to claim 33,wherein connecting the disruption circuit comprises connecting a circuitwhich injects noise at the at least one first frequency band.